In perinatal medicine, severe obesity of the mother occurs in approximately 1% of cases. This is a problem of increasing importance because of the rising prevalence of juvenile obesity. Our retrospective cohort study aimed at characterising high-risk pregnancies associated with morbid obesity (body mass index [BMI]> or =40). This is of interest not only from an epidemiological perspective and for developing guidelines for clinical care but also from an anthropological point of view. We analysed the German perinatal statistics of the years 1998-2000 with data from more than 500,000 pregnancies. Pregnant women with coexistent morbid obesity were compared to a normal weight reference sample with regard to gestational, perinatal and neonatal risks. Birth weight percentiles were used to classify the neonates according to size (hypotrophy if <10th, hypertrophy/foetal macrosomia if >90th). The obtained risk profile for morbidly obese pregnant women primarily showed pregnancy related diseases, such as hypertension, pre-eclampsia and gestational diabetes. Hypertension and signs of foetal hypoxaemia occurred at higher frequencies with morbid obesity. Hypertrophic neonates were born 3.3 times more often to obese mothers than to mothers of the normal weight. At a BMI> or =40 the rates of complications such as pre-eclampsia, gestational diabetes, impending foetal hypoxaemia, foetal macrosomia, as well as neonatal infections and hyperbilirubinaemia were significantly higher. Obesity and maternal comorbidities, accounted for a higher rate of caesarean sections of up to 38.4% at a BMI> or =45. All differences were highly significant. Preconceptionally, the therapeutic approach should be weight reduction.